One of the most powerful and widely-used tools in photo editing is the clone brush, also known as the “clone stamp.” The clone brush permits interactive copying and pasting from one region of an image to another via a brush interface. It is often used to remove undesirable portions of an image, such as blemishes or distracting objects in the background, or to replicate parts of a photograph. The brush interface facilitates fine user control, and interactively copying and pasting existing pixels enables the user to maintain photo-realism even with drastic modifications.
Despite its utility and versatility, the traditional clone brush suffers from several important limitations. First, only regions with similar orientation and distance with respect to the camera can be brushed effectively. Perspective foreshortening present in most photographs and various shapes of the objects in the scene make it difficult to clone brush effectively. Although the traditional clone brush works well for regions of an image that do not have a strong geometric structure, such as clouds or vegetation, many structured features are not amenable for the traditional clone brush due to perspective foreshortening, such as buildings or tiled floors.
Second, intensity variations due to existing lighting in the photograph further limit the effectiveness of the traditional clone brush. Artifacts appear when the intensity of the source and destination regions do not match. Only regions with similar intensities can be clone brushed convincingly using the traditional clone brush.
Third, it may be difficult to manually align the source and destination positions using a traditional clone brush. Misalignment between source and destination features leads to noticeable artifacts at the limit of the clone-brushed region. A precise initialization of source and destination points is often necessary, especially for images that have structured features, such as edges. It is common for the user to undo and repeat the initialization step until the points are sufficiently accurate.
While numerous software packages (such as ADOBE PHOTOSHOP, by Adobe Systems Incorporated, of San Jose, Calif.) provide clone brushing capabilities in an image-editing environment, none of these packages adequately addresses the problems of perspective foreshortening, color correction, or accurately aligning source and destination positions.
What is needed, therefore, is editing software which allows clone brushing that accounts for perspective foreshortening and lighting differences within the image. A need further exists for editing software that allows a user to accurately align source and destination positions for clone brushing.